Insights into the solid-liquid interface of ionic liquid-immobilized solid acid catalyst for isobutane alkylation

The hydrophobic surface modification of solid acids can modulate the interfacial behaviors for isobutane alkylation. Herein, the interfacial properties between isobutane/butene mixtures and immobilized chloroaluminate ionic liquids with different alkyl chain lengths (e.g., ethyl, butyl, hexyl, and octyl groups) on silica substrates were studied through molecular dynamics simulations. The immobilization of ILs leads to obvious aggregation of C4 reactants and improves molar ratio of isobutane to 2-butene (I/O) at the interface, e.g., SiO2[EPIm][Al2Cl7] (I/O = 1.17) versus pure SiO2 (I/O = 0.77) systems. With the prolonged alkyl chain of cations, the interfacial thickness gradually increases, while the I/O molar ratio exhibits the opposite order. Despite the inhibited diffusion of C4 reactants by immobilized ILs, the relative diffusion of isobutane to 2-butene is improved as the alkyl chain of cations prolongs. The above information suggests that the immobilization of ionic liquids with butyl groups is a good choice for isobutane alkylation.